Debtbound by Blood

Kim Sang-an is a ruthless loan shark whose life shatters when his younger sister, a dedicated schoolteacher, dies by suicide following relentless bullying from her students. Consumed by grief and a thirst for vengeance, he infiltrates the very school she taught in, taking over as the homeroom teacher of the tormentors responsible. As a man who always collects what is owed, Sang-an intends to extract the ultimate price for his sister's life, teaching these students the true meaning of debt and retribution.